Self assessment tax calculators and other tax calculators

Reviewed by Mike Parkes, technical director at GoSimpleTax.

HMRC self assessment tax return

Tax calculators can be a useful tools for tax planning and cash flow forecasting. A self assessment tax return calculator can help you assess how much income tax you need to pay if you're a sole trader and pay tax via self assessment. They can also help you estimate future tax bills, so that you can arrange financing if needed. You can also use tax calculators to check payments for past tax years

There are different calculators to help you with different tax liabilities. An income tax calculator, for example, can help you estimate future tax bills, while a company car tax calculator can help you compare the tax impact of different company car choices.

Remember: any calculator will have limitations and cannot take into account your detailed personal circumstances. If you want a detailed picture of your self assessment tax liabilities, you should take advice from your accountant, particularly if you are self-employed.

Here is a round-up of the best tax calculators available online, including those from official bodies such as HMRC and the Valuation Office.

Self assessment tax return calculators

If you use HMRC's Self Assessment online service, tax calculations will be handled automatically (so you will not need a calculator.) You can 'view your calculation' once you have completed the details in the return, but before you submit the return. Once you have submitted the return, your final tax calculation will be available in your online personal tax account within 72 hours.

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Capital gains tax calculators

You may need to pay capital gains tax (CGT) if you sold assets and made a gain greater than the annual exempt allowance (£3,000 in 2024/25). Different allowances applied in previous tax years. You can use these tax calculators and tools to work out how much taxable gain you have, and what CGT is payable:

 

Sole trader v Ltd company tax calculator

 

Income tax and National Insurance calculators

The HMRC self-assessment ready reckoner provides an estimte of income tax and Class 4 NICs. You can get a clearer idea of your tax liabilities by completing your tax return online or by taking advice from your accountant.

If you own a personal services company, you can assess the extra tax and NICs you may have to pay on dividend payments using the IR35 - deemed payment calculator and guidance.

The rules on IR35 have changed, so do your research. If in doubt, always take advice from a qualified accountant.

 

Payroll calculators

HMRC provides a range of calculators you can use when managing payroll deductions:

 

Company car tax calculators

 

Corporation tax calculators

Corporation tax calculations are generally complex, relying on detailed information about income and expenses. Various online tax calculators can help with simple guidance and estimates:

For a fuller assessment of your tax liability, you should take advice.

 

VAT calculators

 

Property tax calculators

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